The present invention relates to a driver-controlled contaminant purging apparatus for use in draining air tanks or compartments of a pressurized pneumatic reservoir of a vehicle such as a truck or a bus and a method of using same in testing the integrity of an air brake system of the vehicle. More specifically, the apparatus allows the vehicle operator to single-handedly test functionality of the air service brake system from within a driver area of the vehicle such test typically being referred to as a pre-trip air system inspection.